Chat scroll bar is offset

The bug

The scroll bar in the chat is no longer where it used to be. It has shifted a bit to the right, causing it to slightly obscure text in chat.

Screenshots are attached, comparing the different versions.

How to reproduce

1. In 21w08b, repeatedly send chat messages until the scroll bar appears
   ✔ The scroll bar is shown against the edge of the screen

2. In 21w10a, repeatedly send chat messages until the scroll bar appears
   ❌ The scroll bar is shifted to the right